The disclosure relates to gas turbine engines. More particularly, the disclosure relates to manufacture of disks.
In typical manufacture of nickel-based superalloy disks (e.g., for gas turbine engine turbine sections or high pressure compressor (HPC) sections), manufacture is by forging of powder metallurgical (PM) or cast forms.
In distinction, only casting techniques are typically used to form blades, vanes, and combustor panels. Many blades are manufactured by single crystal casting techniques. In an exemplary single crystal casting technique, a seed of single crystal material is used to define a crystalline orientation that propagates into the cast blade alloy as it cools and solidifies.
In casting blades, etc., it is well known that removal of high angle grain boundaries (<10°) in single crystal nickel base superalloys leads to improved creep resistance and consequently enhances its temperature capability. In addition, it is also known that by properly orienting the low modulus <100> direction along the direction in which high thermal strain exists, the thermal mechanical fatigue (TMF) capability of the material can also be significantly improved.
However, direct application of nickel base superalloy single crystal to a component such as a turbine disk, has not been practical. This is so because loading of such components due to high rotation speed around an axis is axially symmetric and will lead to uneven strain distribution in a single crystal body, with cubic symmetry and anisotropic elastic and plastic properties.
One method to achieve an axially symmetric ring is to bond separately cast single crystal segments. This has been considered by U.S. Pat. No. 8,206,117 B2 entitled “Turbine component and method of manufacturing turbine component”, by Strangman and Tolpygo. However, this approach requires bonding between circumferential segments, in the high temperature area, which is likely to create weak points.
Another approach is described in U.S. Pat. No. 6,969,240 B2 entitled “Integral turbine composed of a cast single crystal blade ring diffusion bonded to a high strength disk”, by Strangman. A single crystal rim is cast along with single crystal blades and then diffusion bonded to a high strength conventional disk. This approach relies on casting the bladed ring using a large number of discrete single crystal seeds such that presence of high angle grain boundaries is avoided. In this approach, for example, if one wishes to limit the grain boundary misorientation to 10°, then ideally 360°/10°=36 discrete single crystal seeds may be required.